Denim blue jeans which have been faded, "stone-washed", ice washed, or sand blasted to produce a particular appearance are very popular. However, to produce the desired effect it has been necessary to utilize processes which cause substantial deterioration or degradation of the fabric. Bleaching solutions containing chlorine or actual pelleting of the garment with sand or stones to produce a fashion effect causes damage to the fabric which affects its wear life.
The woven goods that are made into denim are typically manufactured from warp yarns (yarns that are in the machine direction on the loom) that have been dyed with Indigo (CI vat blue 1). The crosswise or filling yarns are typically undyed. The yarns are woven in such a way so as to place a high proportion of the colored (blue dyed) yarns on the face of the fabric. This is typically done by weaving the yarns using one of the twill weaves. The result is a fabric which is characteristically known as "Blue Jeans" when fabricated into garments. It has been discovered that bleaching of the Indigo color by one of a number of techniques can lead to desirable styling effects. Several of the bleaching or decolorizing treatments involves potassium (or sodium) permanganate. This compound is the agent of choice when obtaining staying effects by the acid wash or stone wash technique.
Occasionally, garments which have been treated by these methods undergo yellowing during storage of the garments during warehousing and prior to shipment to the retailer or while in the retailers possession if he stores them for any length of time.
The precise causes for the yellowing phenomena is not known. Several possible causes have been identified to include finishing agents (added to the garment to provide a softer hand etc.), atmospheric pollutants or to degradation products associated with the permanganate reactions which are not properly removed during the treatments among other causes. However, not all garments will be yellowed in a particular lot or shipment. The yellowing phenomena may not manifest itself until after the garments have been stored or shipped to the customer. Most likely the yellowed garments do emanate from a particular laundry cycle or machine; however, after the treated garments are removed from the machine the garments from the affected treatment cycle may then become mixed with those from other machines such that their processing lot identity becomes lost. Usually the contaminated (yellow) garments are returned to the seller or are sold at a considerably reduced price.
Various systems have been developed to treat fabric or garments with ozone. The systems generally use steam mixed with ozone enriched air or oxygen and the fabric or garments are suspended in a treatment chamber. The steam has the function of wetting the fabric or garments and to elevate the temperature to increase the reaction rate.
U.S. Pat. No. 1,823,352 to Crespi et al discloses an apparatus for bleaching textile fibers with a gaseous current, such as ozonized air. In the apparatus, textile material is suspended in a chamber where it is acted on by a gaseous ozonized air mixture which passes through the chamber.
U.S. Pat. No. 4,283,251 to Singh discloses a process relating to the ozone and peroxygen bleaching of cellulosic pulp. The process includes the steps of recycling extract effluent from the bleaching treatment.
U.S. Pat. No. 4,300,367 to Thorsen discloses the treatment of fibers with ozone--steam mixtures by conveying them through an open--ended chamber. The fibers are exposed to the ozone--steam mixture in the horizontal middle section of the chamber where the ozone is centrally introduced.
U.S. patent application Ser. No. 560,357 of Hall et al, which is herein incorporated by reference, discloses the fading of dyed cellulosic garments by the ozone degradation of the dye without any substantial degradation of the cellulosic materials in a vapor phase.
It should be understood that the term "dye" as used herein is meant to include any of the materials which are used to provide a color to a fabric such as conventional dyes, pigments, or the like. The term "fabric" as used herein is meant to include woven and non-woven cloth, knitted fabrics, garments, and the like.
It should be understood that the term "ozone and steam" as used herein denotes a preferable method of the invention and is meant to include ozone alone or ozone diluted with inert gases.